Louis/Rui chooses to be a Jack-of-All-Stats because a leader must be able to adapt and react to any situation. Choosing a more balanced and versatile skill set so he'll be ready for anything.
Oliver Collins is a very strong Crutch Character who can kill most early enemies in one or two hits. Is it any wonder he becomes a boss after succumbing to bloodlust and turning into a lost?
What Blood Code do you gain from defeating Oliver after he becomes a frenzied lost and looses his mind? Berserker.
Bayonets using ichor instead of regular bullets: Not only would ammunition be difficult to produce in large quantities in the devastated world, they probably wouldn't be powerful enough to do any real damage to creatures like the lost. Ichor on the other hand can be turned into powerful munition's thanks to the Revenant's powers, is plentiful, can be gained by battling enemies, and would not weight them down like regular ammo. Making it a perfect alternative.
Your checkpoints are mistles. Mistletoe is a parasitic plant that attaches to trees and sucks nutrition out of them. In other words, it's a vampire plant.